Least invasive surgical techniques have gained significant popularity because of their ability to accomplish outcomes with reduced patient pain and accelerated return of the patient to normal activities. Arthroscopic surgery, in which the intra-aticular space is filled with fluid, allows orthopedists to efficiently perform procedures using special purpose instruments designed specifically for arthroscopists. Among these special purpose tools are various manual graspers and biters, electrosurgical devices, and powered shaver blades and rotary abraders. Shaver blades having hollow bores are typically removably coupled to a shaver handpiece and are used for cutting, resecting, boring and abrading both soft and hard tissue at the surgical site. An arthroscopic abrader (also known as a burr) generally includes a rotatable inner tube having an abrading head at its distal end and a fixed outer tube for rotatably receiving the inner tube. Abraders are used for abrading or shaping both soft and hard tissue such as bone, cartilage, ligaments, etc. by use of the rotating abrading head. As the tissue is being abraded, debris and fluid are generally drawn or sucked through the rotatable inner tube.
Requirements for a rotary abrader for arthroscopy include a compact size so as to fit through small cannulae, a means for removal of debris, and a configuration which allows the surgeon to access structures within a joint, while retaining good visibility. One requirement for good visibility is the effective removal of debris as it is generated. Another is that the instrument be configured so that the view of the active portion of the abrader in contact with the tissue and the view of the tissue being abraded are not obscured by the instrument.
Rotary abraders for arthroscopy generally have a shield, also called a “hood,” on one side of the distal end of the outer tube to prevent inadvertent injury to tissue in close proximity to the tissue being abraded. The distal end of this hood is angled with respect to the tube axis so as to expose only one side of the burr head. During use, the burr head (the abrading element at the distal end of the rotating inner member) is subjected to significant lateral forces. Although all rotary abraders have a bearing near the distal end of the instrument to support the inner member, lateral deflection of the burr head occurs. Contact between the burr head and the hood is undesirable since the burr will abrade metal from the hood and deposit metallic debris in the joint. Accordingly, it is necessary to leave adequate clearance between the hood and the burr head. The amount of clearance necessary is largely determined by the rigidity of the inner tube and the placement of the distal bearing between the inner and outer tubes. It is desirable to place the distal bearing as close as practical to the burr head to minimize deflection. It is also desirable to make the distal portion of the inner tube as rigid as practical. On currently available rotary abraders, the outer, stationery tube and inner, rotating tube are concentric. Because of this, the diameter of the distal portion of the outer, stationery tube in proximity to the burr head is significantly larger than the diameter of the burr head, so as to have adequate clearance. The required diameter of this portion of the outer tube is determined by the resistance of the burr head to deflection, which in turn is determined by the bearing placement and inner tube distal end construction. While this increased diameter prevents contact between the burr head and the hood, it also restricts the surgeon's access to some structures, and often obscures the surgeon's view of the site being abraded.
Removal of debris from the field is accomplished by aspirating the material from the joint via a lumen in the inner, rotating member which is connected through a means in the handpiece to an external vacuum source. The aspiration of material through the inner member is desirable as this allows easy transfer of the materials from the proximal end of the instrument to the aspiration passage of the handpiece. The manner in which material and fluid enter the lumen at the distal end of the instrument has a large effect on the volume of flow through the instrument and on the frequency with which the instrument clogs. Insufficient flow causes decreased visibility because of residual debris suspended in the intra-articular fluid. Clogging requires that the instrument be removed from the joint and “de-clogged”. The degree of difficulty of clog removal is determined by the instrument design. Even if clog removal is easily accomplished, removing, de-clogging and reinserting the instrument is a nuisance and causes increased procedure times. Aspiration effectiveness, and therefore instrument design, have a large effect on burr efficiency.
Referring to FIGS. 1 through 5, prior art burr 10 has an inner assembly 12 rotatably positioned within an outer assembly 14. Inner assembly 12 has an proximal end 16 forming a hub assembly 18 for engaging the drive element of a powered handpiece, and an elongated tubular portion 20 having an abrading element 22 at its distal end 24. Bearing 26 is positioned near distal end 24 of tubular portion 20 slightly proximal to aspiration port 28 which provides a means of material flow to the lumen 21 of portion 20. Outer assembly 14 has a proximal end 30 forming a hub assembly 32 for removably mounting in a powered handpiece, and an elongated tubular portion 34 having a distal end 36 forming a beveled surface 38. As best seen in FIG. 4, bearing 26 centers distal end 24 of inner assembly 12 within distal end 36 of outer tubular portion 34 so as to maintain clearance 40 between abrading element 22 and shield (hood) 42 formed by distal end 36 and beveled surface 38. Clearance 40 is determined by the diameter 46 of burr head (abrading element) 22, and the inner diameter 47 and wall thickness 48 of outer tubular portion 34. Debris and liquid are aspirated from the region of abrading element 22 along path 44 to lumen 21 via aspiration port 28.
In U.S. Pat. No. 4,842,578, Johnson et al. teach an aspiration method in which material is drawn into the lumen of the inner tube via slots in the inner assembly distal to the bearing—the bearing is moved quite far proximal, thereby increasing the lateral deflection of the burr head during use. This, in turn, necessitates larger clearance between the burr head and the hood, and thus a large hood diameter, which obscures the surgeon's view and access. The relatively small slots in this design would make the instrument prone to clogging.
In U.S. Pat. No. 5,913,867, Dion teaches a rotary abrader with improved aspiration. As with the Johnson device, material is drawn into the lumen of the inner tube via an opening distal to the bearing between the inner and outer tubes. At least a portion of the opening is distal to the proximal end of the angled distal opening in the hood. This allows greater flow volumes and decreased clogging. However, the bearing is still proximal to the opening in the inner tube which allows for greater deflection of the abrading element during use. This necessitates that the hood diameter be significantly greater than the diameter of the burr head.
Vaca et al., in U.S. Pat. No. 6,053,923, teach a rotary abrader construction in which material is drawn into the lumen of the inner tube through axially aligned openings in the inner and outer tubes proximal to the distal end bearing. The inner and outer tubes may have a single opening or multiple openings. The openings admit liquid and tissue when angularly aligned and have a geometry designed to cooperatively cut tissue in the same manner as an arthroscopic shaver blade. The cutting action of the openings is intended to decrease clogging. The design is likely quite effective when the instrument is fully inserted into the joint, however, there will likely be instances in which the openings are obstructed because the burr is not fully inserted into a joint, or the joint is small. In these cases, it will be impossible to aspirate tissue through the instrument.
Grinberg, in U.S. Pat. No. 5,759,185, teaches a rotary abrader in which a lumen within the burr head extends distally such that openings in the troughs between the cutting flutes of the burr intersect the lumen. Debris is sucked into the openings while the burr is cutting tissue and removed from the site. A potential problem with this method is that the burr is rotating at high speed and the centrifugal force would tend to move material away from the openings. Also, it is likely that cavitation would tend to disrupt the flow of material into the openings, and proximally from the openings to the lumen in the inner tube.
Moutafis, in U.S. Patent Publication No. 2003/0055404, teaches a second stationary tube concentrically positioned about the standard stationery tube with a space between the tubes used to aspirate debris. It is likely that this passage would be prone to clogging unless it was made quite large, in which case the instrument diameter would be very large compared to that of the rotating abrading element. This, in turn, requires the use of large cannulae and generally obstructs the surgeon's view.
Moutafis, in U.S. Patent Publication No. 2003/0083681, teaches a distal bearing which does not have continual contact with the inner tube, but rather has contact regions separated by passages through which liquid and debris are aspirated. This allows the bearing to be placed quite close to the burr head as to minimize deflection, however, the decreased bearing surface will likely lead to higher forces between the bearing and the rotating member making galling and the generation of metallic debris more likely. Also, because of size constraints of the outer tube, the passages would be quite small and prone to clogging. Clearing clogs would be problematic since access to the passages is limited by the burr head, and the burr could not be readily disassembled for clearing as the burr head is larger in size than the bearing surfaces thereby preventing the inner portion from being withdrawn proximally.
U.S. Patent Publication No. 2004/0181251 by Hacker et al. describes a rotary abrader with multiple slots in the stationary outer tube proximal to the burr head and proximal to the distal bearing. A burr so constructed has excellent rigidity since the bearing is close axially to the burr head. It has good flow volume because of the number and size of the slots. If one or more slots become clogged by tissue the other slots still pass enough flow to allow the procedure to continue without having to remove and clear the instrument. A drawback of this construction, however, as in the case of the Vaca et al. device, is that the slots may be obstructed by tissue when the instrument is initially inserted into the joint, or when it is used on a small joint.
The rotary abraders previously herein considered may be generally divided into two categories: those which can be disassembled by withdrawing the inner tube proximally from the outer tube, and those which cannot be so dissembled. Most commercially available arthroscopy burrs fit into the first category. A burr which may be disassembled in this manner must of necessity have a bearing which is affixed to the inner member and is larger in diameter than the burr head, or alternatively have a portion of the rotating member proximal to the burr head with a larger diameter than the burr head to engage a bearing of the stationary outer member. The bearing is generally a thin polymeric or metallic layer applied to the inner which prevents galling between the inner and outer members. The inner member diameter is maximized to maximize the inner lumen size so as to increase flow volume and prevent clogging. Clogging, however, generally occurs at the distal end of the instrument, at the opening of the passage proximal to the burr head. The clogging most frequently occurs because soft tissue wraps around the inner member proximal to the burr. On burrs with a single opening, or with multiple openings in close proximity, a clog stops all aspiration of debris from the site and necessitates removal and clearing of the instrument for the surgical procedure to continue.
There is a need for an improved rotary abrader having rigidity, an aspiration means which effectively removes debris without clogging and which can be readily cleared of clogs without disassembly, and enhanced surgeon visibility.
It is accordingly an object of this invention to provide a rotary abrader with high resistance to deflection of the burr head.
It is also an object of this invention to provide a rotary abrader with improved visibility for the surgeon.
It is also an object of this invention to provide a rotary abrader able to produce high aspiration flow rates regardless of the insertion position of the instrument in the joint or the size of the joint.
It is further an object of this invention to provide a rotary abrader which has multiple aspiration openings so as to allow the instrument to be used with one or more openings partially for fully clogged.